| Animal studies indicate that there are architectural and functional changes of lymphatic vessels in spontaneously hypertensive rats,secondary hypertensive rats induced by high salt,and hypertensive rats caused by both of mechanisms.Previous studies have shown that lymphatic vessels play a vital role in the pathogenesis of hemorrhagic shock.Nevertheless,whether or not the performance of lymphatic vessels after hemorrhagic shock in hypertensive condition is identical to that of normotensive individual has not been reported.The angiotensinconverting enzyme(ACE)inhibitors have been widely applied to therapy of hypertension in clinics.Moreover,ACE inhibitors can relieve the endothelial injury,organs dysfunction and vascular hypo-reactivity to vasoconstrictors induced by hemorrhagic shock attack.Therefore,whether a certain relationship is presented between ACE and function of lymphatic vessels in normotensive or hypertensive conditions is worthy to be discussed.Based on a rat model of renovascular hypertension(2-kidney-1-clip,2K1C),using ACE inhibitor enalapril as tool reagent,the mesenteric lymphatic contractility in vivo and ex vivo,the mesenteric lymphatic response to substance P ex vivo was observed in order to explore the role of ACE in the functional changes of lymphatic vessels and the expression of ACE after hemorrhagic shock in normotensive and hypertensive rats.This study may provide experimental bases for the therapy of hemorrhagic shock in normotensive and hypertensive individuals by targeting ACE to control lymphatic function.First,hypertensive rat model was established by 2K1 C method.Healthy male Wistar rats,weighing 200 ± 10 g,allowed to acclimate for 1week,were randomly divided into sham group(sham surgery),hypertension group(a renal artery clip,2K1C),sham plus enalapril treatment group(sham surgery plus treatment with enalapril 10 mg/kg/d for 4 weeks)and hypertension plus enalapril treatment group(2K1C plus treatment with enalapril 10 mg/kg/d for 4 weeks).The systolic blood pressure of rats received 2K1 C surgery is higher than that of rats received sham manipulation significantly.Enalapril treatment started at the 4th week after 2K1 C surgery and exerts its antihypertensive effect significantly at the 6th,7th and 8th week after 2K1 C surgery.These data suggested that renovascular hypertension established by 2K1 C surgery in rats is feasible and enalapril has significant antihypertensive effect.At 8th week after 2K1 C or sham 2K1 C surgery,rats in sham and sham plus enalapril treatment group were conducted by sham hemorrhagic shock procedure(Rats were anesthetized and their femoral arteries and jugular vein were cannulated,but no blood was withdrawn or infused)and rats in shock and shock plus enalapril treatment group were performed by hemorrhagic shock procedure(Rats were anesthetized,and their mean arterial blood pressure was reduced to 40±2 mmHg and maintained for 1.5h,and resuscitation was carried out at the end of the shock period by reinfusing the shed blood plus Ringer's sodium at the volume of the shed blood).At the end of the 1.5 h hypotensive period,3 h after the end of fluid resuscitation,and the corresponding time point of sham shock,the behavior of mesenteric lymphatic vessels was observed in vivo.The contractile frequency(F),contractile index(Index I),contractile fraction(Index II)and lymphatic dynamic index(L.D-Index)were used to assess the contractile activity of lymphatic vessels.The results indicated that at the end of the1.5 h hypotensive period and at 3 h after the end of fluid resuscitation,hemorrhagic shock blunts the contractile frequency andcontractile activity of mesenteric lymphatic vessels in normotensive and2K1 C caused hypertensive rats significantly;the decrease of contractile frequency and contractile activity of mesenteric lymphatic vessels of hypertensive rats is more serious than that of normotensive rats;enalapril can relieve the contractile functional suppression of mesenteric lymphatic vessels caused by 2K1 C inciting hypertension;meanwhile,enalapril also can relieve the contractile functional suppression of mesenteric lymphatic vessels caused by hemorrhagic shock.The study also shown that the contractile function of lymphatic vessels in the late stage of the shock is declined significantly compared with that in the early stage.The results suggested that both of hemorrhagic shock and 2K1 C inducing hypertension can decrease the contractile activity in vivo of the mesenteric lymphatic vessels,moreover,in the presence of hypertension,lymphatic contractile dysfunction induced by hemorrhagic shock is more serious,and Enalapril treatment can alleviate this dysfunction of lymphatic vessels.The next set of experiment,segments of lymphatic vessels was harvested and prepared at the end of the 3 h after fluid resuscitation to investigate the role of enalapril in the lymphatic dysfunction induced by hemorrhagic shock in normotensive and hypertensive rats ex vivo.The end diastolic diameter(EDD),end systolic diameter(ESD)and contraction frequency(CF)and passive diastolic diameter(PD)were measured using a pressure myograph ex vivo,by which fraction of pump flow(FPF),tonic index(TI)and contraction amplitude(CA)were calculated to assess the contractile function of lymphatic vessels.Thereafter,lymphatic segments were bathed by concentration gradient of SP from low to high,the difference value of the CF,FPF,TI and CA before and after SP treatment(?CF,?FPF,?TI,?CA)were measured and used to assess the lymphatic reactivity.The results indicated that hemorrhagic shock can decrease the lymphatic contractility and reactivity of normotensive rats.Compared with that of normotensive rats,both of the lymphatic contractility and reactivityof 2K1 C caused hypertensive rats were significant decreased.Enalapril treatment can improve the lymphatic contractility and reactivity of 2K1 C caused hypertensive rats.Enalapril treatment can improve the lymphatic contractility and reactivity suppressed by hemorrhagic shock in both normotensive and hypertensive rats.However,in the hypertensive conditions,the CF and FPF of isolated lymphatic increased significantly after hemorrhagic shock,which can be blunted by enalapril.While the segments of lymphatic vessels was harvested and prepared,the thoracic duct tissue was taken out to detect the expression of ACE by immunohistochemical staining.The blood samples were collected by the abdominal aorta for the detectation of the Ang II level in plasma.The results indicated that hemorrhagic shock increased the expression of ACE in the lymphatic tissue and the level of Ang II in plasma.Both of the expression of ACE and the level of plasma Ang II of hypertensive rats were significant increased compared with that of normotensive rats,which was inhabited by Enalapril treatment.In addition,enalapril treatment decreased the expression of ACE in the lymphatic tissue and the level of plasma Ang II increased by hemorrhagic shock in both normotensive and hypertensive rats.In order to further observe whether the change of mesenteric lymphatic contraction was related to intestinal histological damage,intestinal tissue was harvested.HE staining was used to observe the changes of intestinal histomorphology in different groups.At the same time,D-lactic acid(D-LA)and intestinal-type fatty acid-binding protein(I-FABP),which were used to reflect the degree of intestinal injury.The results showed that hemorrhagic shock induced the injury of intestinal tissue in normotensive rats.The intestinal tissue injury in 2K1C-induced hypertensive rats were appeared,which was decreased by the Enalapril treatment.In addition,Enalapril treatment decreased the injury ofintestinal tissue induced by hemorrhagic shock in both normotensive and hypertensive rats.In summary,hemorrhagic shock suppresses function of mesenteric lymphatic vessels of normotensive rats,which can be blunted by enalapril,an ACE inhibitor.The lymphatic contractile function decrease in 2K1 C caused hypertensive rats.The decrease of lymphatic contractile function in2K1 C caused hypertensive rats after hemorrhagic shock is more serious than that of shocked normotensive rats.Enalapril treatment can improve the lymphatic function of 2K1 C caused hypertensive rats.These results suggest that ACE plays a certain role in shocked lymphatic dysfunction both of normotensive and 2K1 C hypertensive rats.As the same time,improvement of the lymphatic function decreased the intestinal injury,however,its mechanism should be research furthermore.Targeting ACE,the regulation of lymphatic function after hemorrhagic shock in normotensive and hypertensive conditions may provide a new insight into the prevention of lymphatic dysfunction induced by hemorrhagic shock conditions. |
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